1. Field of The Invention
This invention relates to a cooling bag for use in either cooling a limited part of human body, foods and drinks, various chemicals, cosmetics, biomaterials and the like or keeping those cold, and more particularly to a cooling bag which can exhibit an adequate and long-lasting cooling action effectively for a whole period of service.
2. Prior Art
It is well known to use granular ammonium nitrate, urea, etc. as an endothermic material for a cooling bag because such kind of materials absorb a large quantity of heat when they are dissolved in water. Although they are outstanding endothermic material from view points of their superior heat absorption characteristics, easier handling properties, economical advantages and the like, they begin to dissolve in instantly when water is added hereto due to their high moisture absorption and solubility in water. Then, in a short period of time, all amount of the endothermic material packed in the cooling bag dissolves to form an aqueous solution (solubilities of ammonium nitrate in 100 g. of water at temperatures of 0.degree. C. and 30.degree. C. being 118.3 g. and 241.8 g., respectively), thereby the water poured in the cooling bag is rapidly cooled to a temperature of -2.degree. C. to -10.degree. C. Such an excessively cooled condition in the bag is gradually moderated with a rise in temperature caused by a heat transfer from an object to be cooled such as a limited part of human body as well as an inevitable heat penetration thereinto from ambient environment other than the object and is warmed to a temperature of 0.degree. C., 5.degree. C., 10.degree. C., 20.degree. C. and higher, until the cooling bag is of no use any longer. Accordingly, an adequately cooled condition available as an effective low temperature source lasts only for rather a short period of time after water is poured. Further, the endothermic material such as granular ammonium nitrate, etc. absorbs moisture in the atmosphere due to its high hygroscopic nature during its storage even under a sealed condition in a polyethylene bag. Particularly, when the endothermic material meets with a temperature of 32.5.degree. C. repeatedly during storage, it tends to integratedly coagulate and solidify in the bag to form an undesirably blocked mass thereof, which might cause an aesthetic deterioration as a commodity.
In order to effectively utilize a large quantity of heat of solution generated by the endothermic material such as ammonium nitrate, etc. for a specific usage, it is desirable, as will be described below, to control the apparent solution velocity in water and keep a low temperature of 0.degree. C. to 2.degree. C. or higher, and more preferably a temperature as in refrigerators for a long period of time after water .is poured. A low temperature source capable of keeping such a low temperature is useful for cooling or keeping cold a limited part of human body such as a region of feverish or bruised or where capillary vessels are broken by heavy sports, or convenient for preserving and delivering many kinds of products such as raw creamed cake.